High frequency amplifying system



Jan. 4, 1944.

H; ROMANDER HIGH FREQUENCY AMPLIFYING SYSTEM Filed Aug. 24, 1942 2 Sheets- Sheet 1 INVENTOR... 62 60 ia/ua/vpfi? ATTORAZEK Jam 1944- H. ROMANDER 2,338,542

I v 7 HIGH FREQUENCY AMPLIFYING SYSTEM- Filed Aug. 24; 1942 K 2 Sheets-Sheet 2 INVENTOR. #060 Roma/v25? Arz'omy Patented Jan. 4, 1944 Search Ron HIGH FREQUENCY AMPLIFYING SYSTEM Hugo Romander, North Caldwell, N. J., assignor to Federal Telephone and Radio Corporation, a corporation of Delaware Application August 24, 1942, Serial No. 455,916

6 Claims.

This invention relates to a high frequency amplifying system, and more particularly to a radio frequency amplifier adapted for use at ultra high frequencies.

An object of this invention is to provide an improved high frequency amplifier.

Another object of this invention is to provide a radio frequency amplifier which will be distortionless throughout a wide range of high and ultra high frequencies.

A further object of this invention is to prevent intratube feedback resulting from induced voltages and internal tube capacitances at high frequencies.

A more specific object of my invention is to provide a novel cross-neutralization network in a push-pull radio frequency amplifier for eliminating the effect of induced radio frequency voltages at high frequencies.

These and other objects of this invention will be apparent from the following description of a preferred embodiment and modification of my system, taken in connection with the attached drawings, in which:

Fig. 1 is a circuit diagram of a push-pull radio frequency amplifier using tetrodes and embodying the neutralizing networks of the present invention;

Fig. 2 diagrammatically illustrates the neutralizing networks of the present invention in connection with an amplifying system as illustrated in Fig. 1; and

Fig. 3 is a diagrammatic bridge similar to Fig. 2 illustrating the application of the principles of the present invention to a push-pull amplifier using pentodes.

Fig. 1 illustrates a radio frequency amplifier of conventional type, in which a pair of tetrodes X, Y are connected in push-pull relationship between a pair of tank circuits A and B. The advantages of so-called cross-neutralization in push-pull amplifiers of this type to eliminate the effect of grid-plate capacities of the tube are well known. This cross-neutralization is brought about by connecting the anode of one tube to the grid of the opposite tube, in each case the capacitor having a value which is substantially equal to the grid-plate capacity of the tube to be neutralized. These added capacitors, together with the inter-electrode capacity within the tubes themselves, form a capacity bridge. As shown in both Figs. 1 and 2, such a bridge may be traced from anode P: through capacitor C2 to grid Gy; from thence through the grid-plate capacitance G of the tube Y to the anode P this anode, in turn, is then connected through capacitor C1 to the grid Gx of tube X and thence through grid-plate capacitance C of tube X to the anode Px.

Such a cross-neutralization circuit as has just been described is entirely suitable for push-pull amplifiers using triodes, tetrodes, or pentodes at ordinary frequencies. At high frequencies, particularly at ultra-high frequencies in circuits involving tetrodes or pentodes, a radio frequency voltage caused by the inductance of the interconnecting leads will be produced on the screen and/or suppressor grids which, through the respective screen and suppressor-grid capacitances will tend to cause internal feedback. In order to produce zero R. F. voltage on the screen or suppressor-grid these capacitors C1 and C2 in the ordinary cross-neutralization circuit may be adjusted to proper values, but in this case adjustment must be made for each frequency to maintain a proper balance of the capacitor bridge. To eliminate this adjustment of capacitors C1 and C: for each frequency, and, in fact, to maintain the screen and/or suppressor grids at zero R. F. potential automatically for all frequencies, I have discovered that the proper insertions of additional capacitors forming secondary bridges with the internal capacitances of the tube are suitable for the purpose.

In connection with a push-pull amplifier using a pair of tetrodes, a pair of capacitors C3 and C4 are connected respectively between the screen grid S h of the tube X, and the grid Gy of the tube Y, and between the screen 5; of the tube Y and the grid G, of the tube X. These capacitors have a value which is substantialy equal to the internal screen grid-control grid capacitances C scrg, C ear-g DI the tube to be neutralized. These capacitors together with the internal capacitances 101111 a subsidiary bridge, shown for the sake of clarity, in double weight lines in Figs. 1 and 2. The lead inductance at ultra-high frequencies is indicated in these figures at L, while the voltage induced upon the screen is indicated at V. The auxiliary neutralizing bridge may be traced, in Fig. 2 from SCl'x to Px through anodescreen capacitance C scrp; from Sen; connection is made to Gy through C3. The second arm of the bridge extends irom Gy through C scrg to Sen connected to Py through the screen-anode capacitance C scrp. The other two arms of the bridge consist of capacitor C4 and e act-g.

In the case of the push-pull amplifier using pentodes, there is provided not only the screen grid neutralizing bridge, described above, but an additional capacitor bridge to balance the R. F. voltage on the suppressor grids caused by the effective inductance L of the suppressor grid leads. The additional bridge is illustrated in Fig. 3 in triple-weight lines, this figure also showing the ordinary.cross-neutralization bridge as well as the screen-grid neutralization bridge described in connectioriwith Figs. land 2. As will be seen by a study of Fig. 3, the voltage induced upon the suppressor grids is neutralized by a subsidiary network which, as opposite. armsof a bridge comprises the capacitances C supg and C rus-e, these beingthe suppressor grid-control grid capacitances of the tube. The other opposite arms of. the bridge consist of capacitors Cs and C6 of a value substantially equal to themternal suppressor grid-control grid capacitances of the-tube to beneutralized. This subsidiary neutralization bridge is connected. at two opposite points directly to control grids Gx and Gy, and at the othercorners to anodes PX and Py through the respective suppressor grid-anode capacitances C supp and C sup--p. In this-case the cross-neutralization bridge. for the screen grids remains-the same as in the case of the tetrode circuits illustrated in Figs. 1 and 2, except that two corners of the bridge are connected to the anodes PX and Py through the respective suppressor grid-screen grid and suppressor gridanode capacitances (C sup-scr, C an-p and C supscr, C supp) in series. The principles of the invention as applied to tetrodes are, therefore equally applicable to pentodes or to tubes involving even more electrodes upon which undesirable induced R. F. voltages may appear.

Accordingly, while this invention has been illustrated as applicable to two types of R. F. push-pull amplifiers, it is to be understood that modifications in the proposed network may be made a will occur to those skilled in this art, and that the invention is. not intended to be limited to the precise network illustrated, except as may be required by the claims which follow:

What is claimed is:

1. In a push-pull amplifier of the type in which a pair of substantially similar electron discharge tubes each having a cathode, an anode, a control grid and one or more additional grids between the control grid and the anode, are connected between a load and a source of current of such high frequency that an inductive voltage is produced upon the interconnected additional grids, the combination of means for neutralizing the effect of this induced voltage, comprising a capacitor connected between the additional grid of each tube to the control grid of the opposite tube, each capacitor having a value substantially equal to the control grid-additional grid capacitance of the tube to be neutralized.

2. A neutralized amplifier of the type adapted to be connected between a load and a source of high frequency current, comprising a pair of electron discharge tubes each having a cathode, an anode, a control grid and one or more addi tional grids intermediate the control grid and the anode, means for connecting said tubes in push-pull relationship between said load and high frequency source, a capacitor connected between each control grid and the anode of the opposite tube, each capacitor having a value substantially equal to the anode-control grid capacitance of the tube to be neutralized, and a capacitor connected between each additional grid and the control grid of the opposite tube, said last capacitor having a value substantially equal tothe additional grid-control grid capacitance of the tube to be neutralized.

3. In a push-pull amplifier of the type "in which a pair of substantially similar tetrodes are connected between a load and a source of current of such1'high frequency that an inductive voltage is produced upon the inter-connected screen grids, the. combination of means for neutralizing thisinduced voltage, comprising a capacitor connected between the screen grid of each tube and the control-grid of the opposite tube, each capacitor having a value substantially equal to the control grid-screen grid capacitance of the tube to be neutralized.

. 4. A neutralized amplifier of the type adapted to be connected between a load and a source of high frequency current, comprising a pair of tetrodes, means for connecting said tetrodes in push-pull relationship between said load and high frequency source, a capacitor connected between each control grid and the anode of the opposite tube, each capacitor having a value substantially equal to the anode-control grid capacitance'of the tube to be neutralized, and a capacitor connected between each screen grid and the control grid of the opposite tube, said last capacitor having a value substantially equal to the control grid-screen grid capacitance of the tube to be neutralized.

5. In a push-pull amplifier of the type in which a pair of substantially similar pentodes are connected between a load and a source of current of such high frequency that an inductive voltage is produced upon the interconnected suppressor grids, the combination of means for neutralizing this induced voltage, comprising a capacitor connected between the suppressor grid of each tube and the control grid of the opposite tube, each capacitor having a value substantially equal to the control grid-suppressor grid capacitance of the'tube to be neutralized.

6. A neutralized amplifier of the type adapted to be connected between a load and a source of high frequency current, comprising a pair of pentodes, means for connecting said pentodes in push-pull relationship between said load and high frequency source, a capacitor connected between each control grid and the anode of the opposite tube, each capacitor having a value substantially equal to the anode-control grid capacitance of the tube to be neutralized, a capacitor connected between each screen grid and the control grid of the opposite tube, said last capacitor having a value substantially equal to the control grid-screen grid capacitance of the tube to be neutralized, and a capacitor connected between each suppressor grid and the control grid of the opposite tube, said last capacitor having a value substantially equal to the suppressor grid-control grid capacitance of the tube to be neutralized.

HUGO ROMANDER. 

